$ { \left[\begin{array}{rr}{-1} & {0} \\ {0} & {-2} \\ {-1} & {4}\end{array}\right]+\left[\begin{array}{rr}{2} & {3} \\ {-1} & {4} \\ {0} & {0}\end{array}\right] = {?} } $
Explanation: To find the sum of two matrices, add the corresponding items between each matrix. ${\left[\begin{array}{rr}{-1}+{2} & {0}+{3} \\ {0}+{-1} & {-2}+{4} \\ {-1}+{0} & {4}+{0}\end{array}\right]}$ Now, simplify: ${\left[\begin{array}{rr}{1} & {3} \\ {-1} & {2} \\ {-1} & {4}\end{array}\right]}$